Styrenic block copolymers are described in, for example, U.S. Pat. Nos. 7,625,979; 7,001,956, 7,166,672; and 7,220,798.
U.S. Pat. No. 7,625,979 discloses lithium-terminated polymers of one or more conjugated dienes and of one or more mono alkenyl arenes are coupled by reaction with an alkoxy silane coupling agent having the formula Rx-Si—(OR′)y, where x is 0 or 1, x+y=4, R and R′ are the same or different, R is selected from aryl hydrocarbon radicals, linear alkyl hydrocarbon radicals and branched alkyl hydrocarbon radicals, and R′ is selected from linear and branched alkyl hydrocarbon radicals, such that the resulting polymer composition contains less than about ten weight percent of uncoupled polymer diblock. The polymer compositions are subsequently selectively hydrogenated.
U.S. Pat. No. 7,001,956 discloses articles prepared from novel anionic block copolymers of mono alkenyl arenes and conjugated dienes, and to blends of such block copolymers with other polymers. The block copolymers are selectively hydrogenated and have mono alkenyl arene end blocks and conjugated diene mid blocks. The block copolymer may be blended with at least one other polymer selected from the group consisting of olefin polymers, styrene polymers, amorphous resins and engineering thermoplastic resins.
U.S. Pat. No. 7,166,672 discloses gels prepared from novel anionic block copolymers of mono alkenyl arenas and conjugated dienes, and to blends of such block copolymers with such polymers. The block copolymers are selectively hydrogenated and have A polymer blocks and B polymer blocks wherein A represents a polymer block of a mono alkenyl arene and B represents a polymer block of a conjugated diene. The block copolymer may be combined with tackifying resins, oils and other components to form a gel.
U.S. Pat. No. 7,220,798 discloses lithium-terminated polymers of one or more conjugated dimes and of one or more mono alkenyl arenes that are coupled by reaction with an alkoxy silane coupling agent having the formula Rx—Si—(OR′)y, where x is 0 or 1, x+y=4, R and R′ are the same or different, R is selected from aryl hydrocarbon radicals, linear alkyl hydrocarbon radicals and branched alkyl hydrocarbon radicals, and R′ is selected from linear and branched alkyl hydrocarbon radicals, such that the resulting polymer composition contains less than about ten weight percent of uncoupled polymer diblock. The polymer compositions are subsequently selectively hydrogenated.
However, there is still a need to produce styrenic block copolymers having the appropriate balance of low viscosity, high tensile strength, and/or isotropic mechanical properties.